1. Field of the Invention
The present invention relates to an ultrasonic probe including plural ultrasonic transducers for transmitting and/or receiving ultrasonic waves in an ultrasonic diagnostic apparatus for medical use or structure flaw detection, and a method of manufacturing such an ultrasonic probe.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and make diagnoses. Especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time without exposure to radiation like other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, and so on.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the waves are reflected at a boundary between regions with different acoustic impedances (e.g., a boundary between structures). Typically, an ultrasonic diagnostic apparatus (or referred to as an ultrasonic imaging apparatus or an ultrasonic observation apparatus) is provided with an ultrasonic probe to be used in contact with the object or ultrasonic probe to be used by being inserted into a body cavity of the object. Alternatively, an ultrasonic endoscope of an endoscope for optically observing the interior of the object in combination with an ultrasonic probe for intracavity is also used.
In the ultrasonic probe, for example, a piezoelectric vibrator (piezoelectric element) having electrodes formed on both ends of a piezoelectric material is used as an ultrasonic transducer for transmitting and/or receiving ultrasonic waves. When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts to generate ultrasonic waves. Further, plural vibrators are one-dimensionally or two-dimensionally arranged and the vibrators are sequentially driven by drive signals provided with predetermined delays, and thereby, an ultrasonic beam can be formed toward a desired direction. On the other hand, the vibrator receives the propagating ultrasonic waves, expands and contracts, and generates an electric signal. The electric signal is used as a reception signal of ultrasonic waves.
In an array type ultrasonic probe as described above, a common electrode (ground electrode) and individual electrodes (address electrodes) are provided for the respective elements. In order to lead out wires from the individual electrodes of the respective elements, at least one substrate for wiring is bonded to the electrodes formed on the upper or lower surface of the piezoelectric materials by using a conducting adhesive material.
The structure of a piezoelectric element is basically a single-layer structure in which electrodes are formed on both ends of one piezoelectric material. However, according to microfabrication and integration of piezoelectric elements with recent developments of MEMS (micro electro mechanical systems) related devices, multilayered piezoelectric elements each having plural piezoelectric materials and plural electrodes alternately stacked have been used. In such a piezoelectric element, the capacitance of the multilayered structure as a whole can be made larger by connecting electrodes for applying electric fields to the respective plural piezoelectric material layers in parallel. Accordingly, the rise in electrical impedance can be suppressed even when the size of the piezoelectric element is made smaller.
The multilayered piezoelectric elements used in the ultrasonic probe are roughly classified into (i) elements having internal electrodes with a whole-surface electrode structure and (ii) elements internal electrodes with an alternating electrode structure. In either structure, the internal electrodes are alternately connected to the common electrode and the individual electrodes respectively formed on the upper and lower surfaces of the multilayered piezoelectric element via side electrodes so as to apply electric fields to the piezoelectric materials in the respective layers.
By the way, as the probe is made smaller, the widths of the vibrators included in the array become smaller, the wiring pattern widths on the substrate for individual wiring become narrower, and the spacings between adjacent wiring patterns become narrower, and thus, the work for leading out the individual wires becomes difficult. In order to solve the problem, a technique of connecting the substrate for individual wiring to the piezoelectric elements such that the individual wires are led out from not only one side along the longitudinal direction of the piezoelectric elements but both sides along the longitudinal direction at twice pitch to be arranged in a staggered manner. In the case where the individual wires are led out in such a manner, the individual wires are divided into odd number channels and even number channels at both sides along the longitudinal direction of the piezoelectric elements. Hereinafter, a manner according which the individual wires are led out as described above is called “staggered manner” for convenience. According to the technique, the lead-out parts of the individual wires are alternately formed on both sides of the piezoelectric materials, and the spacings between adjacent electrodes become wider and the workability is improved. However, at the same time, another substrate for individual wiring is bonded on the same side of the common electrode and, if the conducting adhesive flows out when the other substrate for individual wiring is bonded, it is highly likely that the conducting adhesive is short-circuited to the side electrodes of the multilayered piezoelectric element.
In the case of an ultrasonic probe using single-layered piezoelectric elements, especially, the distance between electrodes becomes smaller as the piezoelectric material becomes thinner for higher frequency. If the conducting adhesive is spread out for bonding the substrates for individual wiring, it easily runs along the side surfaces of the piezoelectric materials and causes short-circuit. For example, when the distance between electrodes is 130 μm, the yield is 50%. In the case of using the multilayered piezoelectric elements, the electrodes are also on the side surfaces of the piezoelectric elements and the distance between electrodes becomes extremely small. If the conducting adhesive flows out when the substrates for individual wiring are bonded, the conducting adhesive easily contacts the side electrodes and causes short-circuit.
As a related technology, Japanese Patent Application Publication JP-P2000-117973A discloses a piezoelectric vibrator unit in which even when the widths of piezoelectric vibrators are made narrower, the continuity between the electrodes at the piezoelectric vibrator side and the conducting pattern of flexible tapes is reliably secured and short-circuit due to excessive solder is not caused. The piezoelectric vibrator unit is configured such that the effective continuity widths of the conducting pattern in the connecting part of the flexible tapes are provided wider than the widths of the piezoelectric vibrators and a non-superposing area that does not superpose on the conducting patterns in the connecting part of the piezoelectric vibrators is provided, and thereby, the excessive solder melted at bonding of the conducting patterns is escaped to the non-superposing area.
Further, Japanese Patent Application Publication JP-P2006-320512A discloses an ultrasonic vibrator that provides increased acoustic output by multilayered connection of plural electromechanical conversion elements with connecting members. The ultrasonic vibrator includes electromechanical conversion elements that convert electric signals into mechanical operation to radiate ultrasonic waves, an acoustic matching layer material provided at the ultrasonic radiation surface side of the electromechanical conversion elements, a backing material provided on the opposite surface to the ultrasonic radiation surface side of the electromechanical conversion elements, a connecting member plastically deformed for electric connection to the electromechanical conversion elements, and an insulating member provided on the surface of the connecting member other than the part that is electrically connected.
However, JP-P2000-117973A and JP-P2006-320512A do not disclose prevention of short-circuit to the side electrodes of the multilayered piezoelectric element caused by the conducting adhesive flowing out when individual wires are bonded in the case where the individual wires lead out from the multilayered piezoelectric elements are arranged in a staggered manner.